1. Field of the Invention
The present invention relates to a halftone dot generator and generating method for use in recording an original as a halftone dot image on a photosensitive material by an image scanning/recording apparatus such as an electronic color process scanner.
2. Description of the Prior Art
All conventional halftone dot generators and generating methods for performing such a halftone dot generating processing in any desired screen angle are based on the following idea. Namely, position coordinates (u, v) of an exposure beam on a recording film are converted into virtual screen coordinates (x, y) of a desired screen angle and ruling. A density threshold is read out from a pattern memory in which the density distribution pattern of the virtual screen is previously written, on the basis of the coordinates (x, y). The on/off operation of an exposure beam is controlled by comparing the density threshold as read out with a density value of an image signal corresponding to the position of the exposure beam, to record a desired halftone dot image on the recording film.
FIG. 1 shows an example of the density distribution pattern of a unit halftone dot stored in the pattern memory, wherein a density mountain is so formed on an x-y coordinate plane that the density threshold is uniquely determined for any virtual screen coordinates (x, y).
In the conventional method as hereinbefore described, however, a degree of freedom is restricted in applying different halftone dot configulations such as a circle, a triangle and a square for each specific density range of the image signal, for example, for the purpose of giving a special effect to duplication, since the density threshold can take only one value for each virtual screen coordinates (x, y).